Recently, the LCD displayer has been applied to many electronic productions, such as computer monitor, vehicle LCD monitor, LCD TV, portable IT productions, laptop computer, cell phone, digital camera or PDA. Because of having the advantages such as light weight, small volume and low power consumption, the application of the LCD display has grown greatly in recent years. When being applied in different productions, the LCD driving circuit must take different characters into consideration respectively. For example, when the LCD display is applied for the portable productions, the design of the LCD driving circuit has to pay much effort on the character of low power consumption in order to extend the usable time. In the other hand, if the driving circuit is applied for a large area LCD display, the ability of driving a high load rapidly is very important.
As the improvement of the resolution in the display, the volume of the SRAM inside the LCD driving IC is also increased. When the volume of the SRAM becomes larger, the area of the SRAM is bigger. For reducing the area of the SRAM to decrease the cost, the common solution is replacing the 2-port 8-T SRAM with the 1-port 6-T SRAM of which area is smaller to reduce the area of the SRAM.
When being applied in the LCD driving IC, the SRAM have to continuously output the frame data in a period to maintain the displaying speed of the display, ex. 60 frames per second. While the frame data is outputted from the SRAM, the circuit outside the driving IC sometimes wants to access the SRAM simultaneously. Since the access operation of the SRAM requested from the circuit outside the driving IC is not controlled by the driving IC, the circuits outside the driving IC and the circuits inside the driving IC sometimes access the SRAM simultaneously. However, the 1-port 6-T SRAM has only one I/O port, the circuits outside the driving IC and the driving IC can't access the SRAM simultaneously, and the confliction occurs when the circuits outside the driving IC and the driving IC access the SRAM simultaneously.
In view of the drawbacks of the prior art, the present invention provides a priority control device to overcome the drawbacks of the prior art.